We can see in your picture that the full area is indeed 7×7 tiles, extending 3 tiles from the sprinkler in each direction. The iridium sprinkler waters only 2 tiles in each direction, making a 5×5 area. I think of it as rings, the quality sprinkler does 1 ring, iridium sprinkler does 2 rings, and the pressure nozzle adds a third ring.
However, there are patches within your 7×7 sprinkler area that appear untilled. Most of your greenhouse soil is the light brown color indicating tilled, unwatered soil. Most of the tiles within your sprinkler area are the dark brown color of tilled and watered soil. But those patches of yellowish color within your sprinkler area indicate untilled soil. Is that what your pressure nozzle is doing? Untilling your soil as if you hit it with the pickaxe?